Silicate-containing additives for well bore treatments and associated methods

ABSTRACT

Methods and compositions for use in subterranean operations, and more particularly, additives comprising one or more silicates used to treat tar resident in a well bore, and methods of use, are provided. In one embodiment, the method comprises a method of treating tar resident in a well bore comprising providing a tar-treating additive comprising one or more silicates introducing the tar-treating additive into the well bore; and allowing the tar-treating additive to react with the tar resident in the well bore so as to at least partially reduce the adhesiveness of the tar.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of commonly owned U.S.application Ser. No. 11/027,313 entitled “Silicate-Containing Additivesfor Well Bore Treatments and Associated Methods,” filed on Dec. 30,2004, which is hereby incorporated by reference.

BACKGROUND

The present invention relates to methods and compositions for use insubterranean operations. More particularly, the present inventionrelates to additives comprising one or more silicates used to treat tarresident in a well bore, and methods of use.

Many subterranean operations involve the drilling of a well bore fromthe surface through rock and/or soil to penetrate a subterraneanformation containing fluids that are desirable for production. Suchdrilling operations may include any suitable technique for forming awell bore that penetrates a subterranean formation. Rotary drillingoperations typically involve attaching a drill bit on a lower end of adrillstring to form a drilling tool and rotating the drill bit alongwith the drillstring into a subterranean formation to create a well borethrough which subsurface formation fluids may be produced. In anothermethod of drilling, coiled tubing may be used instead of jointed pipeand the drill bit may be rotated using a downhole motor. Duringdrilling, drilling fluids may be used, inter alia, to lift or circulateformation cuttings out of the well bore to the surface and to cool thedrill bit. Generally, after a well bore has been drilled to a desireddepth, the drillstring may be removed from the well bore, and a varietyof completion and stimulation operations, including cementing,fracturing treatments, sand control treatments, and remedial treatmentsmay be performed.

In the course of drilling operations, the drillstring and/or otherequipment may come into contact with zones of rock and/or soilcontaining tar; in many such operations, it may be desirable to drillthe well bore through these tar-containing zones. However, tar is arelatively tacky substance that may readily adhere to any surface thatit contacts, including the surfaces of the well bore and/or anyequipment utilized during the drilling operation. Tar also may dissolveinto many synthetic treatment fluids used in the course of drillingoperations, increasing the tacky and adhesive properties of the tar. Ifa sufficient amount of tar adheres to surfaces in the well bore ordrilling equipment, it may, among other things, prevent the drillstringfrom rotating, prevent fluid circulation, or otherwise impede theeffectiveness of a drilling operation. In some cases, it may becomenecessary to remove and/or disassemble the drillstring in order toremove accretions of tar, a process which may create numerous cost andsafety concerns. The accretion of tar on drilling equipment and/or inthe well bore also can impede any subsequent operations downhole,including cementing, acidizing, fracturing, sand control, and remedialtreatments.

Existing methods of managing these problems that result from well boretar incursion have not been successful. Some of these methods involveeffecting an increase in hydrostatic pressure in the well bore so as toforce the tar out of the well bore to the surface. However, thisincreased hydrostatic pressure may damage the well bore and/or a portionof the subterranean formation. Other conventional methods utilizetreatment fluids that comprise dispersants, surfactants, and/orsolubilizers, which allow the tar particles to dissolve in or homogenizewith the treatment fluids. However, the tar particles may not be readilyseparated out of the fluid once they have dissolved into or homogenizedwith the fluid. The presence of the tar particles in the treatment fluidmay alter its rheological properties and/or suspension capacity, whichmay limit its use in subsequent operations. Moreover, the addition ofthese dispersants, surfactants, and solubilizers may dramaticallyincrease the complexity and cost of the drilling operation.

SUMMARY

The present invention relates to methods and compositions for use insubterranean operations. More particularly, the present inventionrelates to additives comprising one or more silicates used to treat tarresident in a well bore, and methods of use.

In one embodiment, the present invention provides a method of treatingtar resident in a well bore comprising: providing a tar-treatingadditive comprising one or more silicates; introducing the tar-treatingadditive into the well bore; and allowing the tar-treating additive toreact with the tar resident in the well bore so as to at least partiallyreduce the adhesiveness of the tar.

In another embodiment, the present invention provides a method of Amethod of treating tar resident in a well bore comprising: providing atreatment fluid comprising a base fluid and a tar-treating additivecomprising one or more silicates; introducing the treatment fluid intothe well bore; and allowing the tar-treating additive in the treatmentfluid to react with the tar resident in the well bore so as to at leastpartially reduce the adhesiveness of the tar.

In another embodiment, the present invention provides a method ofdrilling a portion of a well bore in a subterranean formationcomprising: providing a treatment fluid that comprises a base fluid anda tar-treating additive comprising one or more silicates; and drillingat least a portion of the well bore in the subterranean formation.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the embodiments that follows.

DESCRIPTION

The present invention relates to methods and compositions for use insubterranean operations. More particularly, the present inventionrelates to additives comprising one or more silicates used to treat tarresident in a well bore, and methods of use.

The treatment fluids of the present invention generally comprise a basefluid and a tar-treating additive comprising one or more silicates.Examples of suitable silicates include, but are not limited to, sodiumsilicates and potassium silicates. In some embodiments, the tar-treatingadditives may comprise one or more silicates in a water-based solution.In certain embodiments of this type, the silicates may be present in theaqueous solution in an amount of about 40% by weight of the solution. Inother embodiments, the tar-treating additives also may comprise puresilicates (e.g., in solid or liquid form). The tar-treating additivesmay also comprise additional components, inter alia, to enhance theperformance of these tar-treating additives in specific applications.For example, the tar-treating additive may comprise a viscosifier to,among other things, aid in suspending the tar-treating additive in adrilling fluid. Suitable viscosifying agents may include, but are notlimited to, colloidal agents (e.g., clays, polymers, guar gum), emulsionforming agents, diatomaceous earth, biopolymers, synthetic polymers,chitosans, starches, gelatins, or mixtures thereof. In certainembodiments, the tar-treating additive may be present in the treatmentfluids of the present invention in an amount such that the concentrationof silicates in the treatment fluid is at least about 10% by volume ofthe treatment fluid, and up to an amount such that the properties of thetreatment fluid (e.g., viscosity) are altered so that the treatmentfluid is no longer suitable for the particular application. In certainembodiments, the tar-treating additive may be present in the treatmentfluids of the present invention in an amount such that the concentrationof silicates in the treatment fluid is in a range of from about 20% toabout 40% by volume of the treatment fluid. One of ordinary skill in theart, with the benefit of this disclosure, will be able to determine theappropriate concentration of the tar-treating additive in the treatmentfluid of a particular application.

The base fluid utilized in the treatment fluids of the present inventionmay be aqueous-based or non-aqueous-based, or a mixture thereof. Wherethe base fluid is aqueous-based, it may comprise fresh water, salt water(e.g., water containing one or more salts dissolved therein), brine(e.g., saturated salt water), or seawater. Generally, the water can befrom any source, provided that it does not contain compounds thatadversely affect other components of the treatment fluid. Where the basefluid is non-aqueous-based, the base fluid may comprise any number oforganic liquids. Examples of suitable organic liquids include, but arenot limited to, mineral oils, synthetic oils, esters, and the like. Anexample of a suitable commercially-available non-aqueous-based basefluid is ESTEGREEN™ mud, available from Union Oil Company of California.

The treatment fluids of the present invention optionally may compriseadditional additives to enhance the performance of the treatment fluid.The treatment fluids of the present invention may comprise any suchadditional additives that do not adversely react with the silicates orother components of the treatment fluid. Examples of suitable additionaladditives include, but are not limited to, gelling agents, breakers,stabilizers, fluid loss control additives, surfactants, claystabilizers, bactericides, emulsifiers, and the like. One of ordinaryskill in the art, with the benefit of this disclosure, will be able todetermine which additional additives are appropriate for a particularapplication.

Generally, the methods of the present invention comprise allowing atar-treating additive comprising one or more silicates to react with tarresident in a well bore, thereby reducing the adhesiveness of the tar,inter alia, to facilitate removal of that tar from a well bore or othersurface. When the tar-treating additive reacts with tar, it alters theadhesive properties of the tar such that the tar is less tacky and itbecomes more brittle and dirt-like. In applications where it isdesirable to drill through tar encountered in the course of drilling awell bore, drilling through tar altered in this way may yieldtar-cuttings that can be removed more effectively from the well bore.Additionally, tar which is drilled-through may be less likely to flowinto the well bore or the subterranean formation as the plasticproperties of the tar are altered.

In one embodiment, the present invention provides a method of treatingtar resident in a well bore comprising: providing a tar-treatingadditive comprising one or more silicates, introducing the tar-treatingadditive into the well bore, and allowing the tar-treating additive toreact with the tar resident in the well bore so as to at least partiallyreduce the adhesiveness of the tar. Introducing the tar-treatingadditive to the vicinity of a desired portion of the well bore may beaccomplished by a variety of methods known by a person of ordinary skillin the art with the benefit of this disclosure. One example of such amethod comprises pumping water into the well bore, wherein thetar-treating additive is carried into the well bore on the leading edgeof the water. In other embodiments of this method, the additive may bepumped into the well bore while suspended in a treatment fluid (e.g., adrilling fluid). In certain embodiments, the tar-treating additive maybe provided as a “spot treatment,” wherein the tar-treating additive ispumped into the well bore to react with tar in a specific portion of thewell bore. In certain embodiments of this type, the tar-treatingadditive may be allowed to react with the tar resident in the well borefor at least a time sufficient to at least partially reduce theadhesiveness of the tar. In some circumstances, this may be more thanabout one hour. In others, more time will be required to at leastpartially reduce the adhesiveness of the tar, depending upon, amongother factors, the temperature inside the well bore and the amount oftar in the portion of the well bore being treated. One of ordinary skillin the art, with the benefit of this disclosure, will be able todetermine the appropriate amount of time to allow the tar-treatingadditive to react with the tar according to these factors. An example ofone of these “spot treatment” embodiments, as tested in a laboratoryexperiment, is described below in Example 1. In certain embodiments,after the tar-treating additive has been allowed to react with the tar,the tar then may be removed from the well bore by any means practicablefor the given application.

In another embodiment, the present invention provides a method oftreating tar resident in a well bore comprising: providing a treatmentfluid comprising a base fluid and a tar-treating additive comprising oneor more silicates, introducing the treatment fluid into the well bore,and allowing the tar-treating additive in the treatment fluid to reactwith the tar resident in the well bore so as to at least partiallyreduce the adhesiveness of the tar. In certain embodiments of this type,the tar-treating additive may be allowed to react with the tar as longas the treatment fluid is present in the well bore. One of ordinaryskill in the art, with the benefit of this disclosure, will be able todetermine the appropriate amount of time to allow the tar-treatingadditive to react with the tar so as to at least partially reduce theadhesiveness of the tar. An example of one such treatment employing atreatment fluid of the present invention, as tested in a laboratoryexperiment, is described below in Example 2. In certain embodiments,after the tar-treating additive has been allowed to react with the tar,the tar then may be removed from the well bore by any means practicablefor the given application.

In another embodiment, the present invention provides a method ofdrilling a portion of a well bore in a subterranean formationcomprising: providing a treatment fluid that comprises a base fluid anda tar-treating additive comprising one or more silicates; and drillingat least a portion of the well bore in the subterranean formation. Incertain embodiments, tar may be present within the well bore, and thetar-treating additive may be allowed to react with the tar so as to atleast partially reduce the adhesiveness of the tar. In certainembodiments, after the tar-treating additive has been allowed to reactwith the tar, the tar then may be removed from the well bore by anymeans practicable for the given application.

To facilitate a better understanding of the present invention, thefollowing examples of specific embodiments are given. In no way shouldthe following examples be read to limit or define the entire scope ofthe invention.

EXAMPLES Example 1

The methods of the present invention were tested in the laboratory usingsamples of tar commonly found in the Gulf Coast region. A 200 g-sampleof tar was placed in each of three 350 mL lab barrels, along with asteel rod that had been weighed previously. Then, 55.97 g of a clay-freesynthetic-based drilling fluid was added to the first lab barrel (Barrel1A), 51.52 g of 20% calcium chloride aqueous solution was added to thesecond lab barrel (Barrel 1B), and 55.53 g of a tar-treating additivecomposed of 40% sodium silicate (by weight) in aqueous solution wasadded to the third lab barrel (Barrel 1C). The lab barrels then weresealed and placed in a hot rolling oven at 150° F. for 16 hours.Afterwards, the lab barrels were removed from the oven, and theircontents were removed. The steel rods were weighed in order to determinethe mass of tar still adhered to the rods. The results of these testsare summarized in Table 1 below.

TABLE 1 Post- Mass of Initial rolling tar rod rod mass adhered Barrelmass (g) (g) to rod (g) Observations 1A 340.79 377.54 36.75 Mud hasdissolved into the tar. Tar is tacky to the touch and has a firmconsistency. Tar adhered to the rod cannot be scraped away easily. 1B343.30 359.31 16.01 Tar has a thick, pasty consistency that does notadhere to the rod in a rigid/solid block. Tar is moist and pliable tothe touch. The tar that is present on the rod is scraped away relativelyeasily as a thick paste rather than a hard cake. 1C 342.21 342.72 0.51Tar is hard and brittle and does not adhere to the rod. Thick cake ispressed against the walls of the cell but is removed relatively easilyas a brittle solid. Tar has a dry, crumbly consistency that forms acoarse powder.

Example 2

In this example, a 200 g-sample of tar recovered from the Gulf Coastregion was placed in each of three 350 mL lab barrels, along with asteel rod that had been weighed previously. Then, 51.97 g ESTEGREEN™ mudwas added to each of the first and second lab barrels (Barrels 2A and2B). Additionally, 10 g of DEEPTREAT™, a wetting agent and thinnercommercially available from available from the Baroid Division ofHalliburton Energy Services, Inc., Houston, Tex., was added to the firstlab barrel (Barrel 2A). A heavy emulsifier package, composed of 9 gLEMUL™ and 3 g SUPERMUL, commercially available from available from theBaroid Division of Halliburton Energy Services, Inc., Houston, Tex., wasadded to the second lab barrel (Barrel 2B). Finally, 25.98 g ESTEGREEN™mud and 27.76 g of a tar-treating additive composed of 40% sodiumsilicate (by weight) in aqueous solution were added to the third labbarrel (Barrel 2C). The lab barrels then were sealed and placed in a hotrolling oven at 150° F. for 16 hours. Afterwards, the lab barrels wereremoved from the oven, and their contents were removed. The steel rodswere weighed in order to determine the mass of tar still adhered to therods. The results of these tests are summarized in Table 2 below.

TABLE 2 Mass of Initial Post-rolling tar rod rod adhered to Barrel mass(g) mass (g) rod (g) Observations 2A 340.46 358.09 17.63 Tar has formeda hard-packed coating on steel rod. Tar has a very firm and tackyconsistency. Tar is not removed easily from steel rod, but can bescraped away in firm chunks. Tar is more compact/firm than withtreatments with ESTEGREEN alone (as in Example 3 below). Mud is fullydissolved into tar. 2B 340.75 380.56 39.81 Tar has formed a thick, firmtar coating on surface of steel rod. Tar has a tacky, oily consistencythat is attached to steel rod. Tar can be scraped from surface of rod asa highly viscous paste. Tar is not as firm a coating compared toESTEGREEN alone (as in Example 3 below), but more tacky. 2C 342.13342.15 0.02 No appreciable presence of tar on steel rod surface. Tar isslightly oily in consistency but is still brittle and a packed layercovers the cell wall. Compared to treatment without a mud (see Barrel 1Cin Example 1 above), tar is not as dry but still does not exhibit anysurface tackiness. Tar is removed from inner cell wall easily and can becrumbled with minimal force.

Example 3

In this example, a pre-weighed steel rod was placed in a 350 mL labbarrel, to which 100 g tar recovered from the Gulf Coast region and25.98 g ESTEGREEN™ mud were added. The lab barrel was sealed and placedin a hot rolling oven at 150° F. for 16 hours. Afterwards, the labbarrel was removed from the oven, and its contents were removed. Thesteel rod was weighed in order to determine the mass of tar stilladhered to the rod. These measurements are shown in the first row ofTable 3 below. Then, 65.53 g of a tar-treating additive composed of 40%sodium silicate (by weight) in aqueous solution was added to the labbarrel, as well as the former contents of the lab barrel. The lab barrelwas re-sealed and placed in the same hot rolling oven for another 16hours, after which the steel rod was removed and weighed. Thesemeasurements are shown in the second row of Table 3 below.

TABLE 3 Post- Mass of Initial rolling tar Barrel rod rod mass adhered toContents mass (g) (g) rod (g) Observations tar + ESTEGREEN 343.17 373.3530.18 As previously noted, tar readily adheres to the surface of the rodand has a firm, tacky consistency. tar + ESTEGREEN + 343.17 343.66 0.49Steel rod is notably absent of adhered tar-treating tar. Tar has aslightly oily nature with a additive firm and crumbly consistency. Taris not as dry as seen when treated solely & directly with tar-treatingadditive (see Barrel 1C in Example 1 above). Most closely resembles tartreated with 50/50 ESTEGREEN/tar-treating additive fluid (Barrel 2C inExample 2 above).

Example 4

In this example, 100 g of tar recovered from the Gulf Coast region,25.98 g ESTEGREEN™ mud, and a pre-weighed steel rod were placed in a 350mL lab barrel. The lab barrel was sealed and placed in a hot rollingoven at 150° F. for 16 hours. Afterwards, the lab barrel was removedfrom the oven, and its contents were removed. The steel rod was thenweighed in order to determine the mass of tar still adhered to the rod.These measurements are shown in the first row of Table 4 below. Then,the former contents of the lab barrel were returned to it, and 65.53 gof a tar-treating additive composed of 40% sodium silicate (by weight)in aqueous solution was added. The lab barrel was re-sealed and placedin the same hot rolling oven. The contents of the lab barrel wereremoved after 2 hours, 4 hours, 7 hours, and 71 hours, and the contentsof the lab barrel were observed and recorded at each of those times.These observations are summarized in Table 4 below.

TABLE 4 Post-rolling Mass of tar Initial rod rod adhered Time (hrs) mass(g) mass (g) to rod (g) Observations 0 340.41 379.76 39.35 As previouslynoted, tar readily adheres to the surface of the rod and has a firm,tacky consistency. 2 340.41 347.81 7.40 After 2 hours of hot-rollingwith the tar-treating additive, the tar had become pasty in texture witha majority of the accreted tar no longer attached to the steel rod. 4340.41 348.97 8.56 The tar continues to exhibit a pasty texture with nonoticeable change in composition since the 2-hour mark. 7 340.41 341.190.78 Tar was fully removed from rod. Tar still has a pasty, oilyconsistency and has been packed on the inside of the cell. 71 340.41340.64 0.23 Rod remains free of accreted tar following extensivehot-rolling with the additive treatment.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Whilenumerous changes may be made by those skilled in the art, such changesare encompassed within the spirit of this invention as defined by theappended claims.

1. A method comprising: providing a tar-treating additive comprising oneor more silicates; introducing the tar-treating additive into a wellbore; and allowing the tar-treating additive to react with tar residentin the well bore so as to at least partially reduce the adhesiveness ofthe tar.
 2. The method of claim 1 wherein the tar-treating additivecomprises a water-based solution of the one or more silicates.
 3. Themethod of claim 1 further comprising removing the tar from the wellbore.
 4. The method of claim 1 wherein the tar-treating additive furthercomprises a viscosifier.
 5. The method of claim 1 wherein the silicatescomprise at least one silicate selected from the group consisting of:sodium silicate, potassium silicate, and any derivatives thereof.
 6. Themethod of claim 1 further comprising the step of drilling at least aportion of the well bore.
 7. The method of claim 1 wherein the silicatesare present in an amount in the range of from about 20% to about 40% byvolume of the tar-treating additive.
 8. The method of claim 1 whereinthe step of allowing the tar-treating additive to react with tarresident in the well bore so as to at least partially reduce theadhesiveness of the tar comprises allowing the tar-treating additive toreact with the tar for at least about an hour.
 9. A method comprising:providing a treatment fluid comprising a base fluid, and a tar-treatingadditive comprising one or more silicates; introducing the treatmentfluid into a well bore; and allowing the tar-treating additive in thetreatment fluid to react with tar resident in the well bore so as to atleast partially reduce the adhesiveness of the tar.
 10. The method ofclaim 9 further comprising removing the tar from the well bore.
 11. Themethod of claim 9 wherein the tar-treating additive further comprises aviscosifier.
 12. The method of claim 9 wherein the tar-treating additiveis present in the treatment fluid in an amount such that theconcentration of silicates in the treatment fluid is at least 10% byvolume of the treatment fluid.
 13. The method of claim 9 wherein thetar-treating additive is present in the treatment fluid in an amountsuch that the concentration of silicates in the treatment fluid is inthe range of from about 20% to about 40% by volume of the treatmentfluid.
 14. The method of claim 9 wherein the silicates comprise at leastone silicate selected from the group consisting of: sodium silicate,potassium silicate, and any derivatives thereof.
 15. The method of claim9 wherein the base fluid comprises at least one fluid selected from thegroup consisting of: an aqueous-based fluid, and a non-aqueous-basedfluid.
 16. The method of claim 9 wherein the treatment fluid furthercomprises at least one additive selected from the group consisting of: agelling agent, a breaker, a stabilizer, a fluid loss control additive, asurfactant, a clay stabilizer, a bactericide, and an emulsifier.
 17. Amethod comprising: providing a treatment fluid that comprises anaqueous-based fluid and a tar-treating additive that comprises one ormore silicates selected from the group consisting of sodium silicate,potassium silicate, and any derivatives thereof, wherein thetar-treating additive is present in the treatment fluid in an amountsuch that the concentration of silicates in the treatment fluid is inthe range of from about 20% to about 40% by volume of the treatmentfluid; introducing the tar-treating additive into a well bore; andallowing the tar-treating additive to react with tar resident in thewell bore so as to at least partially reduce the adhesiveness of thetar.
 18. The method of claim 17 further comprising removing the tar fromthe well bore.
 19. The method of claim 17 wherein the tar-treatingadditive further comprises a viscosifier.
 20. The method of claim 16wherein the treatment fluid further comprises at least one additiveselected from the group consisting of: a gelling agent, a breaker, astabilizer, a fluid loss control additive, a surfactant, a claystabilizer, a bactericide, and an emulsifier.